1. Field of the Invention
The present invention relates to a numerical controller for controlling machine tools and various industrial machines, and more particularly, to a numerical controller for controlling a machine tool and the like based on table format data.
2. Description of the Related Art
There is known a numerical control method (so-called electronic cam control) of machine tools, in which a feed axis position and a spindle position synchronized with reference values are stored in a memory in a table form as command data so as to correspond to the reference values rather than commands from respective blocks of a NC program, to control the feed axis position, the spindle position, and the like, based on the table format data stored in the memory. In operations based on table format data, the position of a axis synchronized with a reference value can be controlled accurately even when the speed of advance of the reference value changes, and a tool can operate freely regardless of a machining program unlike the conventional method. In this way, machining time is reduced and machining accuracy is improved. Time, a feed axis position or a spindle position, and the like are used as the reference values (see Japanese Patent Application Publication No. S59-177604). Further, a control method in which command positions in the table format data are connected by quadratic, cubic, quartic, and quintic functions so as to prevent shocks and vibration in machines is also known (see Japanese Patent Application Publication No. 2003-303005 and Japanese Patent Application Publication No. 2007-304714).
Moreover, a control method in which the same reference values are used in the table format data of each axis to be controlled and different reference values are used for respective items of task objects is also known (see Japanese Patent Application Publication No. 2012-234445). Further, Japanese Patent Application Publication No. 2012-234445 also discloses a method in which, when a machine tool is operated based on table format data and an operation of a machine tool to be controlled lags, standby of respective control axes and the like is performed, so that the control axes and the like are controlled in a synchronized manner.
In table format data-based operations, when the accuracy of the table format data output by a CAM is poor, the velocity between respective command positions changes greatly, and it may be difficult to process a machining surface smoothly.
FIG. 1 is a block diagram of table format data-based operations known in the conventional art (disclosed in Japanese Patent Application Publication No. 2003-303005 and Japanese Patent Application Publication No. 2007-304714). In the example illustrated in FIG. 1, X and Z axes are synchronized with reference values. A numerical controller that performs operations based on command data stored as table format data includes a reference value counter 3 that counts signals that form a reference value such as time, a spindle position, and a feed axis position, an X-axis path table Tx, a Z-axis path table Tz, an X-axis path table interpolation process unit 4x, a Z-axis path table interpolation process unit 4z, a feed axis X-axis servo motor 5x, and a feed axis Z-axis servo motor 5z. The X-axis path table Tx and the Z-axis path table Tz are provided in a memory in a numerical controller or a storage device connected to the numerical controller via a network. The X-axis position corresponding to a reference value as command data and the Z-axis position corresponding to the reference value are set and stored in the X-axis path table Tx and the Z-axis path table Tz as table format data, respectively. Hereinafter, the command data stored in the respective axis path tables will be referred to as path table data. The X-axis path table interpolation process unit 4x and the Z-axis path table interpolation process unit 4z read table format data stored in the X-axis path table Tx and the Z-axis path table Tz based on a reference value which is an input value of the reference value counter 3, performs an interpolation process, and outputs the interpolated table format data to the X-axis servo motor 5x and the Z-axis servo motor 5z so that the X-axis and Z-axis servo motors 5x and 5z are driven with the X-axis and Z-axis positions synchronized with the reference value.
For example, when such path table data as illustrated in FIG. 2 is stored in the X-axis path table Tx and the Z-axis path table Tz and a work piece is processed by a machine tool which is controlled based on the path table data by a numerical controller, the tool path follows such a path as illustrated in FIG. 3.
The X-axis position and the Z-axis position are at the point of origin “0.000” when the reference value is L=0.0, and the X and Z axes are driven so that the X-axis position moves from the point of origin to reach the position “0.200” when the reference value reaches L=100.0 and the Z-axis position moves from the point of origin to reach the position “3.000” when the reference value reaches L=150.0. As a result, at the point in time when the reference value reaches L=100.0, the X-axis position is “0.200” and the Z-axis position reaches the position “2.000” in the course of moving so as to reach the position “3.000” when the reference value is L=150.0. That is, the X-axis and Z-axis positions reach P1(X,Z)=(0.200,2.000) at the reference value L=100.0. The X-axis is driven so that the X-axis position moves from the position P1 to reach the position “3.000” at the reference value L=200.0 and to reach the position “1.600” at the position P2 corresponding to the reference value L=150.0 at which the Z-axis position reaches the target position “3.000”. The Z-axis is driven so that the Z-axis position moves from the position P2 to reach the position “0.000” at the reference value L=200.0 and the X-axis position and the Z-axis position reach the positions P3 “3.000” and “0.000”, respectively, at the reference value L=200.0.
Although machining is performed according to such a tool path, since the velocity changes abruptly at the point of origin, the positions P1 and P2, and the position P3, shocks may occur and streaks may appear on a finished surface of a work piece.
In order to eliminate this problem, according to Japanese Patent Application Publication No. 2003-303005 and Japanese Patent Application Publication No. 2007-304714, the command positions are connected by quadratic to quintic function curves, and the tool is moved along the curves to thereby prevent the occurrence of shocks and to obtain a smooth finished surface. However, in the methods disclosed in Japanese Patent Application Publication No. 2003-303005 and Japanese Patent Application Publication No. 2007-304714, although a smooth finished surface can be obtained since a command tool path is corrected by connecting all command positions by quadratic to quintic function curves, users have to correct the path table data in order to apply the methods to existing path table data.